Scientists are peering millions of years back into a supernova's past

CAASTRO
Thirty years ago, an exploding star 168,000 light years away appeared as a small pinpoint of light in the night sky.

The supernova, known as SN 1987A, occurred in a neighboring galaxy called the Large Magellanic Cloud.

It was the result of the core of a massive star collapsing under its own gravity, resulting in a stellar explosion that could be seen from Earth.

Since the supernova was first spotted in the sky, astronomers have used different telescopes and different frequencies to piece together the star's recent past. But they were only able to look as far back as the final 20,000-years of the star's long, long life. Considering the star had thrived for millions of years, that's less than a tenth of its life.

Now, astronomers at the University of Sydney have found a way to peer further back into the star's history than ever before, millions of years before its violent blowout. And it's a huge step in advancing our understanding of these spectacular cosmic explosions.

CAASTRO
The findings were published on Monday in the Monthly Notices of the Royal Astronomical Society, Oxford University Press.

The researchers, led by Joseph Callingham, a PhD candidate at the University of Sydney and the ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), used a telescope array in the Australian desert where there was no FM radio interference.

Using the telescope, they were able to listen to faint hisses emanating from the supernova remnant. This allowed them to investigate the supernova at lower radio frequencies than ever before to help "fine-tune our understanding of stellar explosions," a University of Sydney press release writes.

Usually, scientists can't tell what's happening at these low radio frequencies because signals from our own earthbound FM radio drown out the faint signals from space. But, according to Bryan Gaensler, a professor at the University of Toronto who supervised the research, by studying the strength of the radio signal, astronomers can finally figure out things such as the density of the surrounding gas.

This will allow them to understand the environment of the star before its explosive death.

"Just like excavating and studying ancient ruins that teach us about the life of a past civilization, my colleagues and I have used low-frequency radio observations as a window into the star's life," Callingham said in the press release.

While previous studies focused on material spit out into space when the star was in its final phase, called its blue supergiant phase, the researchers were able to look further back to when the star was in its long-lasting red supergiant phase.

It's rare for a massive star to enter a blue supergiant phase before it collapses. Most stars are in a red supergiant phase of their life when they explode into supernovae. It's important for scientists to study this phase because most stars spend their final stages of life as a red supergiant.

The researchers found that younger material from the blue supergiant, as well as the shock of the supernova explosion, pushed out older material from the red supergiant.

They also learned that the red supergiant lost its matter at a slower rate, and generated slower winds that pushed into its surrounding environment, than scientists had previously guessed.

These new insights improve our knowledge of the composition of the space where SN 1987A spent its life. This will allow scientists to tweak their models and simulations to better reconstruct the physics of supernova explosions, Callingham said.

"Supernova remnant 1987A, more than any other supernova remnant, has shaped our understanding of how massive stars end their lives," Callingham said. "The study has revealed what occurred right before the star's death, helping us to understand the physical processes that led to one of the largest explosions in our universe."